The kernel is the essential center of a computer operating system, the core that provides basic services for all other parts of the operating system. A synonym is nucleus. A kernel can be contrasted with a shell, the outermost part of an operating system that interacts with user commands.The kernel uses system calls such as 'read' and 'write' to provide an abstraction of your hardware. From a programmer's viewpoint, these look just like ordinary function calls, although in reality a system call involves a distinct switch in the operating mode of the processor from user space to kernel space.